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Cycadophyta
Fossil range: Early Permian–Recent
Cycas circinalis with old and new male cones.
Cycas circinalis with old and new male cones. Cycas circinalis, also known as the Queen Sago, is a type of Cycad that was thought to be linked with the degenerative disease Lytico-Bodig disease
Scientific classification
Kingdom: Plantae
Division: Cycadophyta
Class: Cycadopsida
Order: Cycadales
Dumortier
Families

Cycadaceae cycas family
Stangeriaceae stangeria family
Zamiaceae zamia family
Leaves and male cone of Cycas revoluta
Leaves and male cone of Cycas revoluta

Cycads are a group of seed plants characterized by a large crown of compound leaves and a stout trunk. Plants are living Organisms belonging to the kingdom Plantae. Barthélemy Charles Joseph Baron Dumortier (born on April 3, 1797 in Tournai; died in 1878 was a Belgian Politician and Cycas is the Type genus and the only genus currently recognised in the Cycad family Cycadaceae. Stangeriaceae is the smallest family of Cycads both in number of living and Fossil species The Zamiaceae are a family of Cycads that are superficially palm or fern-like Cycas revoluta ( sago cycad) is an attractive plant native to southern Japan. The spermatophytes (from the Greek word "Σπερματόφυτα" (also known as phanerogams) comprise those Plants that produce Seeds They are In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. In Botany, trunk (or bole) refers to the main structural member of a Tree that supports the Branches and is supported by and directly attached They are evergreen, gymnospermous, dioecious plants having large pinnately compound leaves. In Botany, an Evergreen plant is a plant having leaves all year round Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are Plant sexuality covers the wide variety of Sexual reproduction systems found across the Plant kingdom They are frequently confused with and mistaken for palms or ferns, but are related to neither, belonging to the division Cycadophyta. Arecaceae or Palmae (also known by the name Palmaceae, which is taxonomically invalid or commonly palm tree) the palm family is a family of Flowering A fern is any one of a group of about 20000 Species of Plants classified in the phylum or division Pteridophyta, also known as Filicophyta

Cycads are found across much of the subtropical and tropical parts of the world. They are found in South and Central America (where the greatest diversity occurs), Mexico, the Antilles, south-eastern United States of America, Australia, Melanesia, Micronesia, Japan, China, Southeast Asia, India, Sri Lanka, Madagascar, and southern and tropical Africa, where at least 65 species occur. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. The Antilles (the same in French; Antillas in Spanish; Antillen in Dutch) refers to the islands forming the greater part of the The United States of America —commonly referred to as the For a topic outline on this subject see List of basic Australia topics. Melanesia (from Greek: μέλας black, νῆσος island) means "islands of the black-skinned people" Micronesia, from the Greek mikros (μικρός (meaning small) and nesos (νῆσος (meaning island) is a Subregion For a topic outline on this subject see List of basic Japan topics. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka ( Sinhalese:, இலங்கை known as Ceylon before 1972 is an Island Madagascar, or Republic of Madagascar (older name Malagasy Republic) is an Island nation in the Indian Ocean off the southeastern Southern Africa is the Southernmost Region of the African Continent, variably defined by Geography or Geopolitics. Some are renowned for survival in harsh semi-desert climates, and can grow in sand or even on rock. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere They are able to grow in full sun or shade, and some are salt tolerant. For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a Though they are a minor component of the plant kingdom today, during the Jurassic period they were extremely common. The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning Sago flour is generally made from true palms – not from the cycad popularly known as "Sago Palm" (Cycas revoluta). Sago is a Starch extracted from the Pith inside stems of the sago palm Metroxylon sagu Cycas revoluta ( sago cycad) is an attractive plant native to southern Japan.

They have very specialized pollinators and have been reported to fix nitrogen in association with a cyanobacterium living in the roots. A pollinator is the biotic agent ( vector) that moves Pollen from the male Anthers of a Flower to the female stigma of a flower to accomplish Nitrogen fixation is the process by which Nitrogen is taken from its natural relatively inert molecular form (N2 in the atmosphere and converted into Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy This blue-green algae produces a neurotoxin called BMAA that is found in the seeds of cycads. Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy A neurotoxin is a Toxin that acts specifically on nerve cells ( Neurons, usually by interacting with Membrane proteins such as Ion channels β-methylamino L-alanine, or BMAA, is a Neurotoxin found in the seeds of the Cycad. A seed (in some plants referred to as a kernel) is a small embryonic Plant enclosed in a covering called the seed coat usually with some stored

Contents

Origins

The cycad fossil record dates to the Early Permian, 280 mya. The Permian is a geologic period and system that extends from 299 In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". There is controversy over older cycad fossils that date to the late Carboniferous period, 300–325  mya. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 One of the first colonizers of terrestrial habitats, this clade probably diversified extensively within its first few million years, although the extent to which it radiated is unknown as relatively few fossil specimens have been found. The regions to which cycads are restricted probably indicate their former distribution on the supercontinents Laurasia and Gondwana. Laurasia (lɔˈreɪʃiə lɔˈreɪʒə was a Supercontinent that most recently existed as a part of the split of the Pangaean supercontinent in the late Mesozoic Gondwana (ɡɒnˈdwɑːnə originally Gondwanaland) was a southern Supercontinent that existed about 500 to 200 Ma ago

The family Stangeriaceae (named for Dr. William Stanger, 1812(?)–1854), consisting of only three extant species, is thought to be of Gondwanan origin as fossils have been found in Lower Cretaceous deposits in Argentina, dating to 70–135 mya. Extant is a term commonly used to refer to Taxa (such as Species, genera or families) that are still in existence (living The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous For a topic outline on this subject see List of basic Argentina topics. Zamiaceae is more diverse, with a fossil record extending from the Middle Triassic to the Eocene (54–200 mya) in North and South America, Europe, Australia, and Antarctica, implying that the family was present before the break-up of Pangea. The Zamiaceae are a family of Cycads that are superficially palm or fern-like The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Eocene epoch (558 ± 02 - 339 ± 01 Ma) is a major division of the Geologic timescale and the second epoch of the Palaeogene period in Pangaea, Pangæa or Pangea (pænˈdʒiːə from παν pan, meaning entire, and Γαῖα Gaea, meaning Earth in Cycadaceae is thought to be an early offshoot from other cycads, with fossils from Eocene deposits (38–54 mya) in Japan and China, indicating that this family originated in Laurasia. For a topic outline on this subject see List of basic Japan topics. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Cycas is the only genus in the family and contains 99 species, the most of any cycad genus. Cycas is the Type genus and the only genus currently recognised in the Cycad family Cycadaceae. Molecular data has recently shown that Cycas species in Australasia and the east coast of Africa are recent arrivals, suggesting that adaptive radiation may have occurred. Australasia is a Region of Oceania: New Zealand, Australia, Papua New Guinea, and neighbouring Islands in the Pacific The current distribution of cycads may be due to radiations from a few ancestral types sequestered on Laurasia and Gondwana, or could be explained by genetic drift following the separation of already evolved genera. In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time Both explanations account for the strict endemism across present continental lines. Endemism is the Ecological state of being unique to a place Endemic species are not naturally found elsewhere

Taxonomy

There are about 305 described species, in 10–12 genera and 2–3 families of cycads (depending on taxonomic viewpoint). Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos The classification below, proposed by Dennis Stevenson in 1990, is based upon a hierarchical structure based on cladistic analyses of morphological, anatomical, karyological, physiological and phytochemical data. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration A karyotype is the characteristic Chromosome complement of a Eukaryote Species. Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical Phytochemistry is in the strict sense of the word the study of Phytochemicals These are chemicals derived from Plants In a narrower sense the terms are often used Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's

The number of species in the clade is low compared to the number of species in most other plant phyla. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. However, paleobotanical and molecular research indicates that diversity was higher in the history of the phylum. Fossil evidence shows that structural diversity in Mesozoic cycad pollen "considerably exceeds that seen in surviving genera today". The Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The impacts of extinction on diversity are highlighted below. The disparity in molecular sequences is very high between the three main lineages of cycads, implying that genetic diversity in the clade was once high, but this fact has led to major disagreements about the divisions within the Cycadales.

The number of described cycad species has doubled in the past 25 years, mostly due to improved sampling and further exploration. Experts assume there may still be about 100 undescribed species, based on the rate of discovery. These are likely to be in Asia and South America where areas of endemism are highest. Diversity hotspots also occur in Australia, South Africa, Mexico, China and Vietnam, which together account for more than 70% of the world’s cycad species. A biodiversity hotspot is a Biogeographic region with a significant reservoir of biodiversity that is threatened with destruction The Republic of South Africa (also known by other official names) is a country located at the southern tip of the continent of Africa Vietnam (ˌviːɛtˈnɑːm Việt Nam) officially The taxonomy of the Cycadophyta is, however, now stabilizing.

Cycad systematists reject the biological species concept, as clearly defined cycad species can interbreed and produce fertile offspring; this character is thus not disproportionately weighted when determining species barriers. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. In Biology, hybrid has two meanings The first meaning is the result of interbreeding between two animals or plants of different taxa. The phenetic species concept, which states that a species is defined based on overall similarities with other individuals of the same species combined with a significant gap in variation with other species, is also rejected. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Most cycad taxonomists agree on a modified version of the evolutionary species concept, termed the ‘morphogeographic’ species concept, which recognises the combined effects of geographical isolation and morphological disparity. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Thus the presence of large geographical gaps in cycad distribution has greatly affected the way cycads are classified.

Suborder Cycadineae
Family Cycadaceae
Subfamily Cycadoideae
Cycas. Cycas is the Type genus and the only genus currently recognised in the Cycad family Cycadaceae. Cycas is the Type genus and the only genus currently recognised in the Cycad family Cycadaceae. About 90 species in the Old World from Africa east to southern Japan, Australia and the western Pacific Ocean islands; type: C. circinalis L. The Old World consists of those parts of Earth known to Europeans Asians and Africans in the 15th century The Pacific Ocean is the largest of the Earth 's Oceanic divisions Cycas circinalis, also known as the Queen Sago, is a type of Cycad that was thought to be linked with the degenerative disease Lytico-Bodig disease ; see also C. pruinosa and C. revoluta
Suborder Zamiineae
Family Stangeriaceae
Subfamily Stangerioideae
Stangeria. Cycas pruinosa is a small to medium species of Cycad. It is a widespread but sporadic species in the eastern and southern Kimberley region of Cycas revoluta ( sago cycad) is an attractive plant native to southern Japan. Stangeriaceae is the smallest family of Cycads both in number of living and Fossil species Stangeria eriopus is a Cycad endemic to southern Africa It is the sole species in the genus Stangeria, most closely related to the One species in southern Africa; type: S. eriopus (Kunze) Baillon
Subfamily Bowenioideae
Bowenia. Stangeria eriopus is a Cycad endemic to southern Africa It is the sole species in the genus Stangeria, most closely related to the The genus Bowenia, includes two living and two Fossil species of Cycads in the family Stangeriaceae, and is entirely restricted to Australia Two species in Queensland, Australia; type: B. spectabilis Hook. Queensland is a state of Australia, occupying the north-eastern corner of the mainland continent UserPolbot. --> Bowenia spectabilis is a species of Plant in the Stangeriaceae family ex Hook. f.
Family Zamiaceae
Subfamily Encephalartoideae
Tribe Diooeae
Dioon. The Zamiaceae are a family of Cycads that are superficially palm or fern-like Dioon is a plant Genus of 11 described Species. They are Cycads in the family Zamiaceae, and native to Mexico, Ten species in Mexico and Central America; type: D. edule Lindley
Tribe Encephalarteae
Subtribe Encephalartinae
Encephalartos. Dioon edule is a cycad native to Mexico, also known as palma de la Virgen. Encephalartos is a genus of Cycad native to Africa. Several species of Encephalartos are commonly referred to as bread palms, About 60 species in southeast Africa; type: E. friderici-guilielmi Lehmann, E. transvenosus (Modjadji cycad)
Subtribe Macrozamiinae
Macrozamia. Encephalartos transvenosus ( Modjadji Cycad or Modjadji's Cycad) is a palm -like Cycad in the family Zamiaceae, growing Macrozamia is a genus of 38-40 species of Cycads in the family Zamiaceae, endemic to Australia. About 30 species in Australia; type: M. riedlei (Fischer ex Gaudichaud) C. UserPolbot. --> Macrozamia riedlei (common name Zamia or Zamia Palm) is a species of Plant A. Gardner
Lepidozamia. Lepidozamia is a genus of two species of Cycad, native to Australia. Two species in eastern Australia; type: L. peroffskyana Regel
Subfamily Zamioideae
Tribe Ceratozamieae
Ceratozamia. UserPolbot. --> Lepidozamia peroffskyana is a species of Plant in the Zamiaceae family Ceratozamia is a genus of New World Cycads in the family Zamiaceae. 16 species in southern Mexico and Central America; type: C. mexicana Brongn. UserPolbot. --> Ceratozamia mexicana is a species of Plant in the Zamiaceae family
Tribe Zamieae
Subtribe Microcycadinae
Microcycas. Microcycas is a genus of Cycads in the family Zamiaceae containing only one species Microcycas calocoma, endemic to a small area One species in Cuba; type: M. calocoma (Miquel) A. The Republic of Cuba (ˈkjuːbə or) consists of the island of Cuba (the largest and second-most populous island of the Greater Antilles) Isla de la Microcycas is a genus of Cycads in the family Zamiaceae containing only one species Microcycas calocoma, endemic to a small area DC.
Subtribe Zamiinae
Chigua. Chigua is a genus of Cycads in the family Zamiaceae containing two species endemic to small areas in northwestern Colombia. Two species in Colombia; type: C. Colombia (kəˈlʌmbɪə officially the Republic of Colombia () is a country in northwestern South America. restrepoi E. Stevenson
Zamia. Zamia is a genus of Cycad of the family Zamiaceae containing around 50 species native to North, Central and South America. About 60 species in the New World from Georgia, USA south to Bolivia; type: Z. pumila L. The State of Georgia ( is a state in the United States and was one of the original Thirteen Colonies that revolted against British rule The Republic of Bolivia (República de Bolivia) named after Simón Bolívar, is a Landlocked country in central South America. Zamia pumila, or Coontie, is a small tough woody Cycad of the West Indies and Cuba. ; see also Z. furfuracea

Cycads are most closely related to the extinct Bennettitales, and are also relatively close relatives to the Ginkgoales, as shown in the following phylogeny:

Phylogeny of anthophytes and gymnosperms, from [1]

Cycads



Ginkgo



Conifers

Anthophytes

Bennettitales


Gnetales


Angiosperms






Angiosperms





Cycads


Bennettitales



Ginkgo




Conifers


Gnetales



Traditional view Modern view

History

Modern knowledge about Cycads began in the 9th century with the recording by two Arab naturalists that the genus Cycas was used as a source of flour in India. Zamia furfuracea is a Cycad native to southeastern Veracruz state in eastern Mexico. Bennettitales (the cycadeoids) is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward The Ginkgoaceae is a family of Gymnosperms which appeared during the Mesozoic Era of which the only extant representative is Ginkgo biloba The araB gene Promoter is a bacterial promoter activated by e L-arabinose binding Flour is a powder made of Cereal grains It is the key ingredient of Bread, which is a staple food in many countries and therefore the availability Later, in the 16th century, Antonio Pigafetta, Fernao Lopez de Castanheda and Francis Drake found Cycas plants in the Moluccas, where the seeds were eaten. Antonio Pigafetta (c 1491 was an Italian Scholar born in Vicenza. Sir Francis Drake, Vice Admiral, (c 1540 &ndash 27 January 1595 was an English Privateer, navigator, Slaver, and politician The Maluku Islands (also known as the Moluccas, Moluccan Islands, the Spice Islands or simply Maluku) are an Archipelago The first report of cycads in the New World was by Giovanni Lerio in his 1576 trip to Brazil, where he observed a plant named ayrius by the indigenous people; this species is now classified in the genus Zamia. The New World is one of the names used for the non-Eurasian/non-African parts of the Earth specifically the Americas and Australia.

Cycads belonging to the genus Encephalartos were first described by Johann Georg Christian Lehmann in 1834. Encephalartos is a genus of Cycad native to Africa. Several species of Encephalartos are commonly referred to as bread palms, Johann Georg Christian Lehmann ( February 25, 1792 Haselau bei Uetersen Holstein &ndash February 12, 1860 Hamburg was a German Year 1834 ( MDCCCXXXIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common The name is derived from the Greek articles "en", meaning "in", "cephale", meaning "head", and "artos", meaning "bread". Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly

Throughout the 18th-19th centuries, discoveries of several species were reported by numerous naturalist researchers and discoverers traveling throughout the world. One of the most notable researchers of cycads was American botanist C. Botany, plant science(s, phytology, or plant biology is a branch of Biology and is the scientific study of plant Life J. Chamberlain whose work is noteworthy for the quantity of data and the novelty of his approach to studying cycads. His 15 years of travel throughout Africa, the Americas and Australia to observe cycads in their natural habitat resulted in his 1919 publication of The Living Cycads which remains current in its synthesis of taxonomy, morphology and reproductive biology of cycads, most of which was obtained from his original research. Year 1919 ( MCMXIX) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common His 1940s monograph on the Cycadales, though never published (most likely because of his death) was never used by botanists. A monograph ( Classical Greek, "One Writer" or "Single Writing") is a work of writing upon a single subject usually also by a single There are no other complete works on the cycads.

Uses

The generic name refers to the starch obtained from the stems which was used as food by some indigenous tribes. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an Tribal people grind and soak the nuts to remove the nerve toxin, making the food source generally safe to eat, although often not all the toxin is removed. A toxin ( Greek:, toxikon, lit (poison for use on arrows is a Poisonous substance produced by living cells or organisms that is active at very low In addition, consumers of bush meat may face a health threat as the meat comes from game which may have eaten cycad nuts and carry traces of the toxin in body fat. Bushmeat ( Calque from the French viande de brousse) is the term commonly used for Meat of terrestrial wild animals killed for Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water

There is some indication that the regular consumption of starch derived from cycads is a factor in the development of Lytico-Bodig disease, a neurological disease with symptoms similar to those of Parkinson's disease and ALS. Lytico-Bodig disease, sometimes spelt Lytigo-bodig is a neurological disease that exists on the Island of Guam. Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the Central nervous system that often impairs the sufferer's Lytico-Bodic and its potential connection to cycasin ingestion is one of the subjects explored in Oliver Sacks' 1997 book Island of the Colourblind. Oliver Wolf Sacks, CBE (born July 9, 1933, London is a British Neurologist residing in the United States who has written popular books about

Distribution

Approximate world distribution of living Cycadales
Approximate world distribution of living Cycadales

Overall species diversity peaks at 17˚ 15"N and 28˚ 12"S, with a minor peak at the equator. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the There is therefore not a latitudinal diversity gradient towards the equator but towards the tropics. The pattern The increase in species richness or Biodiversity that occurs from the Poles to the Tropics, often referred to as the latitudinal gradient However, the peak in the northern tropics is largely due to Cycas in Asia and Zamia in the New World, whereas the peak in the southern tropics is due to Cycas again, and also to the diverse genus Encephalartos in southern and central Africa and Macrozamia in Australia. Thus the distribution pattern of cycad species with latitude appears to be an artifact of the geographical isolation of cycad genera, and is dependent on the remaining species in each genus that did not follow the extinction pattern of their ancestors. Cycas is the only genus that has a broad geographical range and can thus be used to infer that cycads tend to live in the upper and lower tropics. This is probably because these areas have a drier climate with relatively cool winters; while cycads require some rainfall, they appear to be partly xerophytic. A xerophyte or xerophytic organism ( xero meaning dry phyte meaning plant is a Plant which is able to survive in an ecosystem with little available Potted specimens are found and thrive in global locations such as Canada, Russia, Finland, Chile. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending Finland, officially the Republic of Finland ( is a Nordic country situated in the Fennoscandian region of northern Europe. Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the

Speciation

There are no documented cases of sympatric speciation in cycads and allopatry appears to be the most common form of speciation in the group. Sympatric speciation is the genetic divergence of various populations (from a single parent species inhabiting the same geographic region such that those populations become different Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier This is difficult to study as they are long-lived plants, and so natural experiments have been investigated. One example is Cycas seemannii, which occurs only in Fiji, New Caledonia, Tonga and Vanuatu. Fiji (Matanitu ko Viti फ़िजी officially the Republic of the Fiji Islands (Matanitu Tu-Vaka-i-koya ko Viti फ़िजी द्वीप समूह गणराज्य For the former North American fur-trading district see New Caledonia (Canada, and for the Scottish colony in Panama see Darien scheme. The Kingdom of Tonga is an Archipelago in the south Pacific Ocean comprising 169 islands 36 of them inhabited stretching over a distance of about 800 kilometres (500 miles Vanuatu, officially the Republic of Vanuatu ( French: République de Vanuatu, Bislama: Ripablik blong Vanuatu) is an Island Genetic diversity within populations was found to be significantly lower than between islands, suggesting that genetic drift is a likely mechanism for speciation, and is probably currently occurring between the isolated populations. Genetic diversity is a level of Biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a species Allopatry has also been proposed as the mechanism of speciation in Dioon, which predominantly occurs in Mexico. The many rivers that have shaped the region, and repeated glaciation and consequent disjunction, are thought to have been important in reproductive isolation not only in Dioon but in many other plant and animal taxa. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to Parapatric speciation may also have occurred, especially as cycads are pollinated by insects rather than by wind. Parapatric speciation is a form of Speciation that occurs due to variations in mating frequency of a population within a continuous geographical area As the range of the species grows, the individuals furthest apart are prevented from interbreeding as insects have relatively small ranges and will not pollinate between these plants. If sympatric speciation has occurred in cycads this would most likely be because of a host shift in pollinators, due to the very fact that cycads are uniformly dioecious. Plant sexuality covers the wide variety of Sexual reproduction systems found across the Plant kingdom

Extinction

The probable former range of cycads can be inferred from their global distribution. For example, the family Stangeriaceae only contains three extant species, in Africa. Diverse fossils of this family have been dated to 135 mya, indicating that diversity may have been much greater before the Jurassic and late Triassic mass extinction events. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period However, the cycad fossil record is generally poor and little can be deduced about the effects of each mass extinction event on their diversity.

Instead, correlations can be made between the number of extant gymnosperms and angiosperms. Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group It is likely that cycad diversity was affected more by the great angiosperm radiation in the mid-Cretaceous than by extinctions. Very slow cambial growth was first used to define cycads, and because of this characteristic the group could not compete with the rapidly growing, relatively short-lived angiosperms, which now number over 250,000 species, compared to the 947 remaining gymnosperms. It is surprising that the cycads are still extant, having been faced with extreme competition and five major extinctions. The ability of cycads to survive in relatively dry environments where plant diversity is generally lower, and their great longevity may explain their long persistence.

Conservation

Encephalartos woodii is extinct in the wild, and all living specimens are clones of the type
Encephalartos woodii is extinct in the wild, and all living specimens are clones of the type

In recent years, many cycads have been dwindling in numbers and may face risk of extinction because of theft and unscrupulous collection from their natural habitats, as well as from habitat destruction. In biology a type is that which fixes a name to a Taxon. Depending on the nomenclature code which is applied to the organism in question a type may be a specimen In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa.

23% of the 305 extant cycad species are either critically endangered or endangered, and 15% are vulnerable. Organisms with a conservation status of critically endangered have an extremely high risk of becoming extinct An endangered species is a population of an organism which is at risk of becoming Extinct because it is either few in numbers or threatened by changing environmental or predation Thus 38% of cycads are on the IUCN Red List (2004), and the other 62% are in the Least concern or Near Threatened category (i. The IUCN Red List of Threatened Species (also known as the IUCN Red List or Red Data List) created in 1963 is the world's most comprehensive inventory of the global Least Concern ( LC) is an IUCN category assigned to extant species or lower taxa which have been evaluated but do not qualify for any other category Near Threatened ( NT) is a Conservation status assigned to species or lower taxa which may be considered threatened with extinction in the near future although e. not actually on the Red List), or are data deficient. Data Deficient ( DD) is a category applied by the IUCN to a species when the available information is not sufficient for a proper assessment of Conservation status This value has changed dramatically within the past few years; 46% of cycads were on the 1978 Red List, and this rose to 82% in 1997. This was largely due to the recent discovery of over 150 new species, disagreements about classification, and uncertainty. This has not been helpful for conservation planning for the group.

Zamia in the New World, Cycas in Asia and Encephalartos in Africa are the most threatened genera. This pattern reflects the pressures on species in these regions. At least two species, Encephalartos woodii and Encephalartos relictus (both from Africa), are confirmed extinct in the wild. Encephalartos woodii, also known as Wood's Cycad, is a Cycad in the genus Encephalartos, endemic to the Natal Extinct in the Wild ( EW) is a Conservation status assigned to species or lower taxa the only known living members of which are being kept in captivity or as a naturalized Cycads are long-lived with infrequent reproduction, and most populations are small, putting them at risk of extinction from habitat destruction and stochastic environmental events. Regionally, Australian cycads are the least at risk, as they are locally common and habitat fragmentation is low. However, land management with fire is thought to be a threat to Australian species. African cycads are rare and are thought to be naturally decreasing due to small population sizes, and there is controversy over whether to let natural extinction processes act on these cycads.

All cycads are in the CITES appendix appearing under the heading Plant Kingdom and under three family names, Cycadaceae, Stangeriaceae and Zamiaceae. CITES (the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora) is an international agreement between governments drafted

All cycads are CITES APPENDIX II except the following, in APPENDIX I:

Cycad seeds from species on APPENDIX II are not CITES regulated. APPENDIX I seeds are treated the same as the plants.

Horticulture

A Sago Cycad (Cycas revoluta) growing in England as a houseplant
A Sago Cycad (Cycas revoluta) growing in England as a houseplant

Cycads can be cut up into pieces to make new plants, although the most environmentally responsible method is by direct planting of the seeds. Propagation by seeds is the preferred method of growth, and two unique risks to their germination exist. One is that the seeds have no dormancy, so that the embryo is biologically required to maintain growth and development, which means if the seed dries out, it dies. The second is that the emerging radicle and embryo can be very susceptible to fungal diseases in its early stages when in unhygienic or excessively wet conditions. Thus, many cycad growers pre-germinate the seeds in moist, sterile mediums such as vermiculite or perlite. However pre-germination is not necessary, and many report success by directly planting the seeds in regular potting soil. As with many plants, a combination of well-drained soil, sunlight, water and nutrients will help it to prosper. Although, because of their hardy nature, cycads do not necessarily require the most tender or careful treatment, they can grow in almost any medium, including soil-less ones. One of the most common cause of cycad death is from rotting stems and roots due to over-watering.

Some insects, particularly scale insects, some weevils and chewing insects can damage cycads, though the pests are susceptible to insecticides such as the horticulture soluble oil white oil. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described The scale insects are small Insects of the order Hemiptera, generally classified as the Superfamily Coccoidea. A weevil is any Beetle from the Curculionoidea Superfamily. They are usually small less than 6  mm (¼  Inch) and herbivorous An insecticide is a Pesticide used against Insects in all developmental forms Sometimes bacterial preparations may be used to control insect infestation on cycads. However, when some of the mature plants prepare for reproduction, the presence of weevils have been shown to help accomplish pollination.

While the cycads have a reputation of slow growth, it is not always well-founded and some actually grow quite fast, achieving reproductive maturity in 2–3 years (as with some Zamia species), while others in 15 years (as with some Cycas, Australian Macrozamia and Lepidozamia).

References

  1. ^ Crepet, W. L. (2000). "Progress in understanding angiosperm history, success, and relationships: Darwin's abominably "perplexing phenomenon"". Proceedings of the National Academy of Sciences 97: 12939. doi:10.1073/pnas.97.24.12939. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 11087846.  

External links

Dictionary

cycad

-noun

  1. (botany) Any plant of the natural order Cycadaceae, as the sago palm, etc.
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